gridview page indexing problem

hey .. i have a gridview and i set allowpaging=true.
in the first column, i have a check box for choosing items..when i click on the second page of the gridview,
and click a button for update,
it doesn't recognize the changes i made in the previous record on the first page of the gridview.

how will i get the record of the previous page on the grid view even i navigate to many pages in the gridview??

anyway, i managed to remain the checkboxes value even changing page. my problem now is that when i clicked the button for update, it doesn't recognize the previous page of the gridview with checked checkboxes.

i tried debugging it with printing the total number of checkboxes checked and it returns that it doenst include the previous page of the gridview..